1. Field of the Invention
The present invention relates to a surveillance apparatus and method. In particular, although not exclusively, the present invention relates to radar systems including phased array radar systems.
2. Discussion of the Background Art
The principles of phased arrays have been utilized in a number of fields including telecommunications (e.g. AM broadcast stations), radio astronomy and radar systems since the Second World War. Typically such arrays include a number of active radiators coupled to a feed network. The phase of each feed signal supplied to each of the radiators is varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction (i.e. directional beam), while being suppressed in undesired directions.
One type of phased array radar is a planar phased array which has good resolution and overcomes the limitations of mechanically scanned antennas. An example of a planar phased array radar presently in use is the “Aegis” combat system utilized by the United States Navy. At the heart of the Aegis system are several AN/SPY-1 radars each of which is a multi-function planar phased-array radar comprising an array of antenna elements including radiators and receivers, which define a radar aperture. The Aegis system is capable of search, automatic detection, transition to track, tracking of air and surface targets, and missile engagement support.
However a problem with such planar arrays is that they tend to be rather large and cumbersome and prone to wind loading effects, especially in mobile applications. The size and weight of planar arrays generally results from the number of elements populating the radar aperture. The number of elements populating the array is proportional to the area of the aperture needed for a given angular resolution. This makes them exceedingly difficult to mount on board ships and other moving vehicles. Furthermore the cost of producing such arrays is rather prohibitive and accordingly the use of such arrays has all but been limited, for example to a few military applications.
Another problem with the use of a planar phased array is that it typically only covers +/−45 degrees from the bore-sight. This characteristic requires the use of four arrays to provide full 360 degrees of azimuth coverage, such as in the Ageis system.
A number of techniques been utilized in order to overcome the problems associated with conventional phased array radar systems, such as synthetic aperture radar (SAR). In SAR applications a radar antenna is mounted on a fast moving platform whereby movement of the radar antenna enables synthesis of an aperture of a much bigger antenna in one dimension.
Clearly it would be advantageous if a surveillance apparatus and method could be provided that overcomes or at least ameliorates these and other problems of the prior art.